Variables & Control

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Variables

A key aspect of experimental research is the control and measurement of variables.

Any experiment includes two key variables:
- The independent variable — IV — is the variable that the researcher changes, i.e. manipulates. This is done by having a different value of this variable in each experimental condition.
- The dependent variable — DV — is the variable that the researcher measures.
An experiment tries to find out whether the IV has an effect on the DV.

For example, the researcher may compare the effect of using a memory technique on recall of a list of facts.
The use of the technique or not is the IV, and their recall on a test of the facts would be the DV.

To test cause and effect between the IV and DV, it is necessary to keep all other variables constant through controlling confounding variables and minimising effects of extraneous variables.

If an outside variable changes across the two conditions, this becomes a confounding variable and can ruin the experiment.
- In the earlier example, if participants in one condition were given more time to study the facts than those in the other condition, this would be a confounding variable.
- It would make it impossible to be sure whether the IV (memory technique) had had an effect on the DV.

Some variables can’t be entirely eliminated, such as background noise and temperature.
These are called extraneous variables.
The researcher tries to minimise the effects of extraneous variables as far as possible.
Any remaining extraneous variables are a source of random error, but do not invalidate the experiment.

Two further aspects of experimental control are counterbalancing and standardisation.

When a researcher uses a repeated measures design, participants complete two (or more) experimental conditions.
The order in which participants complete the conditions is important.
When they complete the second condition, they may do better due to practice, or worse due to boredom or fatigue.
These are called order effects, and could bias results.

To minimise order effects, experiments use a technique called counterbalancing.
This involves allocating participants to conditions as follows:
- Half of the participants complete condition 1 first, and condition 2 second.
- The other half of the participants complete condition 2 first, and condition 1 second.
Counterbalancing does not get rid of order effects, but it stops order from becoming a confounding variable because the effect is balanced out over the two conditions.

Standardisation means using a standard procedure for all participants. Things which should be standardised include:
- Giving all participants the same instructions.
- Completing briefing and debriefing in the same way and at the same time.
- Conducting the experiment in the same location and at the same time of day.
- Making sure that all materials are the same for all participants.
All aspects of standardisation are necessary to avoid extraneous or confounding variables affecting the results.